1. Field of the Invention
This invention relates to a method of controlling an internal combustion engine mounted on a construction vehicle which can be driven with less fuel consumption and with lower noise level generated by the engine.
2. Description of the Prior Art
In a construction vehicle having an internal combustion engine (referred to simply as "engine" hereinbelow), variable displacement hydraulic pumps driven by the engine to actuate work implements, and means for controlling the flow rate of the fluid delivered by the hydraulic pumps, the arrangement is made such that one of the following three methods has so far been employed when the output fluid flow from the hydraulic pumps is not required for the vehicle.
1. The engine is not controlled; that is, the number of revolutions of the engine is kept at nearly the same level as that when the output fluid flow from the hydraulic pumps is needed. PA1 2. The amount of fuel injected into the engine is controlled immediately to reduce the number of revolutions of the engine. PA1 3. When a predetermined period of time has passed from the time when the output fluid flow from the hydraulic pumps becomes unnecessary, the amount of fuel injected into the engine is controlled to reduce the number of revolutions of the engine.
Each of the above-mentioned methods has respective disadvantage as mentioned below.
Stating in brief, in the case of the first controlling method, the engine is driven at a high speed even when the output fluid flow from the hydraulic pumps is not required so that the fuel is wasted, and the noise level generated by the engine is high.
While, the second controlling method is suitable for the time of completion of the earth moving operation by the construction vehicle. However, in this method, when earth moving operation is made continuously and intermittent supply of the output fluid flow from the hydraulic pumps is required, frequent changes in the rotating speed of the engine occur thus not only having an adverse effect on the engine, but also giving the driver an unpleasant feeling due to changes in the noise level generated by the engine. Further, the forces produced by the hydraulic pumps will cause a surging phenomenon which results in deterioration of component parts.
In the case of the third controlling method, the number of revolutions of the engine is not reduced until a predetermined period of time passes after the output fluid flow from the hydraulic pumps becomes unnecessary. Therefore, the number of revolutions of the engine is initially kept at a value higher than that at the time of normal operation by an amount corresponding to the reduction in the load on the engine so that fuel is wasted and the noise level generated by the engine becomes higher. Further, since, after the lapse of a predetermined time, the number of revolutions of the engine is reduced from a high speed to a low speed, there is a fear that undesirable low speed rotation occurs. Further, in the case where earth moving operation is made which requires intermittent supply of output fluid flow from the hydraulic pumps in the period of time exceeding the above-mentioned predetermined time, a length of time is required to change from a low speed rotation to a desired high speed rotation, thus causing poorer operability and a lowering in operational efficiency.